1. Field of the Invention
The present invention relates to an apparatus for measuring the resistance of an electronic component and, more particularly, to an apparatus suitable for the measurement of the resistance of an electronic component having a small capacity and high resistance.
2. Description of the Related Art
When the resistance of an electronic component such as a capacitor is measured, measuring terminals must be put in contact with electrodes of the electronic component to be tested. A measured value will not indicate the resistance correctly if there is poor contact between the measuring terminals and the electrodes of the electronic component. However, for an electronic component having very high resistance, it is difficult to distinguish the state of poor contact from a normal state.
Insulation resistance measuring apparatuses capable of detecting the contact of the measuring terminals and measuring insulation resistance as shown in FIG. 1 are known (for example, see Japanese unexamined patent publication No. H4-131770). Specifically, 1 and 2 respectively designate a sine wave generator and a DC measuring power supply which are each grounded at one end thereof and one of which is selected by a switch 3 at the other end thereof. The switch 3 is connected to one end of a capacitor 5 to be tested through a current limiting resistor 4, and the other end of the capacitor 5 is connected to an input of an amplifier 6. Measuring terminals 7a and 7b are in contact with electrodes on both ends of the capacitor 5. The output of the amplifier 6 is connected through a switch 8 to an A-D converter 9 which is connected to an analyzer (CPU) 10. The output of the amplifier 6 is also connected to the switch 8 through an RMS-DC converter 11. When the switch 8 is switched to the position of the amplifier, the amplifier 6 is directly connected to the A-D converter 9 and, when the switch 8 is switched to the position of the RMS-DC converter, the amplifier 6 is connected to the A-D converter 9 through the RMS-DC converter 11.
A description will now be made on a method of measuring the insulation resistance of the capacitor 5 to be tested using the measuring apparatus described above.
First, in order to confirm that the capacitor 5 is in proper contact with the measuring terminals 7a and 7b, the switch 3 is switched to the position of the sine wave generator 1 to apply an AC signal having a frequency on the order of, for example, 1 kHz. At the same time, the switch 8 is switched to the position of the RMS-DC converter 11. As a result, the AC signal flows through the capacitor 5, is amplified by the amplifier 6, and is then converted by the RMS-DC converter 11 into a DC signal which corresponds to the RMS value. The DC signal is digitized by the A-D converter 9 and is analyzed by the CPU 10. When this digitized signal is below a reference, it indicates poor contact.
If there is proper contact, the switch 3 is then switched to the position of the DC power supply 2, and the switch 8 is switched to the position of the amplifier 6 at the same time. As a result, the capacitor 5 is charged by a current which is limited by the current limiting resistor 4. After the charging, any leakage current from the capacitor 5 is amplified by the amplifier 6; the output of the amplifier 6 is digitized by the A-D converter 9; and the output of the A-D converter 9 is analyzed by the CPU 10 to calculate the insulation resistance of the capacitor 5.
According to the above-described method of detecting contact, the contact between the measuring terminals 7a and 7b and the capacitor 5 is detected by detecting the capacity of the capacitor 5 by applying an AC signal thereto. However, the detection of contact based on the detection of the capacity as described above has a problem in that reliable detection of contact can not be performed when the tested element 5 has a very small or no capacity.
It is therefore an object of the present invention to provide an apparatus for measuring the resistance of an electronic component capable of reliable detection of contact even for an electronic component to be tested having a small capacity.